As far as I am aware, Muslims must operate within the laws of their hosting country as long as they do not force them to break Islamic laws. This would mean that no Imam in the UK should perform an Islamic marriage with anyone under the age of sixteen.

To have sex with a female she must either be one's wife, or a prisoner of war.

To be bound to condone marriage at such a young age the believer must adhere to the Sunnah of Muhammad. Sunnah is a prescribed normative life based on the actions of Muhammad who, according to the Quran, was the perfect example of a Muslim. This Sunnah is derived from hadiths, which are not part of the Quran but a secondary source of information written some time after Muhammad's death from orally transmitted history.

Some Muslims follow the Quran only so hadiths do not apply to them. There is no reason I know of to be forced to condone sex with such young females from the Quran only, despite the Quranic argument I will put forward (details later).

There are different levels of confidence in Hadith collections. The strongest of these is known as a Sahih (strong) collection, these are what I will use for my references. A hadith in a Sahih collection is considered even stronger of the account is traced back to one of the companions of Muhammad through a different chain of people (Isnad). Not all Muslims accept the references I will provide.

Some Muslims who follow Sunnah and accept the provided references as authentic still disagree with marriage at such a young age for various other reasons.

I felt these points were important to make because I wanted to point out that it is a subset of Muslims who condone marriage and sex with females at such a young age, and that "Muslim rape gangs" are (to my knowledge) operating in violation of these religious laws. More like "a beef eating vegetarian" than the "no true Scotsman" fallacy. Now that I have hopefully disarmed the EDL/Robert Spencer/Pamella Geller type readers, let us begin.

Evidence from the Quran

Before having sex with a female (wife or slave) a Muslim man must first ensure she is not pregnant. This is to ensure the paternities of the children are known. There are various implications of paternity such as how a child should be named, inheritance issues, and slaves who give birth to their master's child cannot be sold and are automatically freed upon the death of their "owner"

Quran 33.49 says that the waiting period (Iddat) for a woman who has not had sex is not applicable. Quran 2.228 says that the waiting period is 3 menstrual cycles. Quran 65.4 specifies the waiting period for women who do not have menstrual cycles, these are as follows

Females who no longer menstruate: Three calendar months

Females who are otherwise not menstruating: Three calendar months

Females who are pregnant: Until they give birth

Obviously a female who has never menstruated can still become pregnant if they ovulate, making their egg available for fertilisation, so they too must have a waiting period if remarrying. Being premenarcheal does not automatically mean a female is young, Amenorrhoea is a condition where females of a reproductive age do not menstruate due to various medical problems. It is because of this that I personally do not feel it is justifiable to say that Islam forces Muslims to condone sex with pre-menarcheal females let alone 9 year old brides if using only the Quran. Whether or not Quran-only Islamic states or individual Muslims do condone such actions is not the point of this article.

Evidence from Hadiths

It is the supporting documents of the hadiths which portray these Quran verses in a less favourable light. Hadiths from Sahih Bukhari[1][2][3] claim that Muhammad married* his wife Aisha when she was 6 and consumated that marriage when she was 9. Hadiths from Sahih Muslim[4][5][6][7] say that Aisha was 6 or 7 when Muhammad married her and she was 9 when taken to his house as his bride. The Sunan Abu Dawud[8][9] collection states Aisha was 6 when married and that she had her first period when she was 9, at which point Muhammad had sex with her. Sunan an-Nasa'i[10][11][12][13][14][15] says that Aisha was 9 years old when Muhammad consummated their marriage. Sunan Ibn Majah[16][17] says that Aisha was 6 when married to Muammad and 9 when that marriage was consummated.

*Note that according to Quran 33.49 the annulment of an unconsummated marriage is immediate, this means that an Islamic unconsummated marriage is akin to an engagement to marry here in the UK, and a consummated marriage is the point at which the marriage becomes the equivalent of a UK marriage.

Evidence from Asbab Al Nuzul by Al-Wahidi

Asbab Al Nuzul is a "collection of circumstances of revelation", it is an attempt to document hadiths related to the events leading up to the revealing of verses. The account of verse 65.4 states

Ubayy ibn Ka"b said: "O Messenger of Allah, of some women of Medina are saying: there are other women who have not been mentioned!" He asked him: "And who are they?" He said: "Those who are too young [such that they have not started menstruating yet], those who are too old [whose menstruation has stopped] and those who are pregnant"

I find it odd that this lack of information needed to be pointed out to Muhammad, who claimed to be receiving the information from an all-knowing entity. I find it more odd that the receiver of divine information from this all-knowing entity had to ask "Who are they?", however that is a different subject, possibly one for a future article. The point is that here the premenarcheal females in question are premenarcheal specifically due to the fact that they are too young.

Exegeses (tafsirs)

Tafsir Al Jalalyn states that those who have not yet menstruated have not done so because they are too young. Tafsir Ibn Abbas (via Tanwir Al-Miqbas) also states that these females are too young to menstruate (note that the authenticity of Ibn Abbas is questioned). Finally Sayyid Abul Ala Maududi has quite a lot to say on the subject, I will quote selectively

They may not have menstruated as yet either because of young age, or delayed menstrual discharge as it happens in the case of some women, or because of no discharge at all throughout life which, though rare, may also be the case...making mention of the waiting-period for the girls who have not yet menstruated, clearly proves that it is not only permissible to give away the girl in marriage at this age but it is also permissible for the husband to consummate marriage with her. Now, obviously no Muslim has the right to forbid a thing which the Qur'an has held as permissible.

Maturity does not imply puberty

As with the marriage/engagement example there are cross language/culture differences regarding the word "puberty". Puberty implies the presence of pubic hair, whereas Islamic puberty does not necessitate this. For this reason I shall use the term "Islamic maturity" instead.

According to this fatwa a girl becomes a woman (and therefore eligible for sex through marriage or slavery) based on her reaching at least the age of 9 (as per the Muhammad/Aisha example) and in addition must meet at least one the following criteria

When pubic hair grows around her private parts

When she starts to menstruate

When she first emits a fluid from her vagina which is associated with having sex

If none of these signs appear by the age of 15 then she automatically reaches Islamic maturity. In addition to this the girl must have the mental competence to be required to perform religious practises such as fasting, praying, and wearing a Hijab.